Migration guide for multiple home units

[Erdi, Gergo]

PUBLIC

In case anyone finds this interesting, I ended up splitting the unit initialization into two parts: one where all units are registered, without any package dependencies, and one where the package dependencies of a single unit are registered. This allowed us to start with just knowing which units are in play, use summariseFile to discover module dependencies, and then use that to compute package dependencies. It's basically just a refactoring of Matt's code from his email up the chain.

setUnits :: [(UnitId, DynFlags -> DynFlags)] -> HscEnv -> IO HscEnv
setUnits units hsc_env = do
    home_unit_graph <- createHomeUnitGraph hsc_env units'
    setHomeUnitGraph hsc_env dummy_home_unit home_unit_graph
  where
    dflags0 = hsc_dflags hsc_env

    units'@((dummy_home_unit, _):_) =
        [ (unit_id, unitFlags dflags0{ homeUnitId_ = unit_id, packageFlags = [] })
        | (unit_id, unitFlags) <- units
        ]

setUnitDeps :: UnitId -> [UnitId] -> HscEnv -> IO HscEnv
setUnitDeps unit_id deps hsc_env = do
    home_unit_env <- fillHomeUnitEnv hsc_env home_units new_dflags
    let home_unit_graph = unitEnv_insert unit_id home_unit_env home_unit_graph0
    setHomeUnitGraph hsc_env unit_id home_unit_graph
  where
    old_dflags = ue_unitFlags unit_id $ hsc_unit_env hsc_env
    new_dflags = old_dflags
        { packageFlags = [ ExposePackage "" (UnitIdArg (RealUnit $ Definite uid)) (ModRenaming True []) | uid <- deps]
        }

    home_unit_graph0 = ue_home_unit_graph . hsc_unit_env $ hsc_env
    home_units = unitEnv_keys home_unit_graph0

setHomeUnitGraph :: HscEnv -> UnitId -> HomeUnitGraph -> IO HscEnv
setHomeUnitGraph hsc_env unit_id home_unit_graph = do
    unit_env <- assertUnitEnvInvariant <$> initUnitEnv unit_id home_unit_graph (ghcNameVersion dflags0) (targetPlatform dflags0)
    return $ hsc_env { hsc_unit_env = unit_env }
  where
    dflags0 = hsc_dflags hsc_env

createHomeUnitGraph :: HscEnv -> [(UnitId, DynFlags)] -> IO HomeUnitGraph
createHomeUnitGraph hsc_env units =
    unitEnv_new <$> traverse (fillHomeUnitEnv hsc_env home_units) (Map.fromList units)
  where
    home_units = Set.fromList $ map fst units

fillHomeUnitEnv :: HscEnv -> Set.Set UnitId -> DynFlags -> IO HomeUnitEnv
fillHomeUnitEnv hsc_env home_units dflags = do
    (dbs, unit_state, home_unit, _) <- initUnits logger dflags Nothing home_units

    pure $ HomeUnitEnv
        { homeUnitEnv_units = unit_state
        , homeUnitEnv_unit_dbs = Just dbs
        , homeUnitEnv_dflags = dflags
        , homeUnitEnv_hpt = emptyHomePackageTable
        , homeUnitEnv_home_unit = Just home_unit
        }
  where
    logger = hsc_logger hsc_env


-----Original Message-----
From: Erdi, Gergo 
Sent: Tuesday, June 21, 2022 5:42 PM
To: Matthew Pickering <matthewtpickering at gmail.com>
Cc: ÉRDI Gergo <gergo at erdi.hu>; GHC Devs <ghc-devs at haskell.org>; Montelatici, Raphael Laurent <Raphael.Montelatici at sc.com>
Subject: Re: Migration guide for multiple home units

Thanks, based on this I got things going. I might have to come back to you if it turns out something's still broken in my original full application.

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